3-D TV disparities said to cause physical, mental strain

Banks recommends two solutions to minimize eye fatigue and other symptoms: Viewers should sit very far from a 3-D TV screen as they would in a theater. The farther from the screen, the smaller the difference between the convergence and the accommodation distances, Banks said.

The second is to shoot 3-D videos so that action is located at the front of the screen, not off one side or projecting out of the screen into a crowd. By minimizing the vergence-accommodation disparity, the possibility of fatigue and other symptoms will recede in most people, according to Banks.

"The better 3-D movies, like Avatar and Pixar's 'Up' are clearly trying to minimize this conflict with the way they do the cinematography," said Banks.

Even if the theater experience is duplicated in the home, not all of the potential problems associated with 3-D TV will be resolved, according to University of Washington professor Robert Patterson. Patterson and Silzars presented their results at the 2009 Society of Information Display. According to the researchers, three other cognitive disparities can cause fatigue in addition to vergence-accommodation: binocular disparity, linear-perspective disparity and texture perspective disparity.

For instance, if a 3-D scene depicts a football player running the length of the field, depth has to be compressed into a few yards by the cinematographer to prevent too much parallax, causing viewers to see double-image ghosting. Linear perspective (geometric angles) and the texture perspective (distant objects that are less detailed) signal the brain that the distance traveled was 100 yards, thereby creating cognitive disparities.

"The reason why high-level cue conflict leads to discomfort in immersive stereo displays is that the intuitive reasoning system is attempting to make reasoned sense out of this incoming, conflicted perceptual information," Patterson and Silzars wrote.

These higher-level cues create conflicts in the brain that causes mental strain in addition to the physical eye strain of the vergence-accommodation disparity, they added, which becomes intolerable over time, resulting in a confused state of mind akin to vertigo.

"When you take away cues, you create in the brain what is called the 'doll house' effect. The scene can be very precisely constructed, but it does not look real--it looks like a doll house--because your brain is saying that its missing cues that are always present when viewing real scenes," said Silzars. "It creates a vision-to-brain conflict that can make you feel nauseous and dizzy or worse."

Worse still, according to Patterson and Silzars, is that the closer a set of cues comes to matching reality, the more discomfort viewers experience. That means the problem could get worse as cinematographers attempt to make 3-D experiences even more realistic. One solution, according to Silzars, would be to confine 3-D content to animations since the brain does not expect cartoons to contain the same realism as normal video or film.

"In Avatar for instance, the scenes that were shot with real backgrounds were less convincing than the animated scenes because the brain has lower expectations for animations," said Silzars.

The brain is very good at rewiring itself to accommodate novel visual effects. The problem is that it might adapt too well, and not adapt back fast enough afterward. Like when driving the car after a long 3D TV session. If this affected only 1 in 1000 people that's still big lawsuits. I think 3D is dead.

When I watched Avatar 3D I noticed some eye strain which will probably be different per person. My 6 year old nephew was sitting next to me he reacted to a couple of early scenes but when the golf ball rolled out he went to sleep soon after. I felt the visual cues that we require in everyday life were missing. Much like trying to fly an airplane under the hood its disorienting. When you see some thing coming in 3D coming at you your reflexes want to move but you tell yourself its only a movie and you don't need to move. I think the brain will adapt. Plus I had little or no disorietation after the movie.

As a stereo photographer I have learned to tolerate the vergence-accommodate disparity, because that is the only way to "free view" side-by-side left-and-right images on stereographic cards without the need for glasses. You just stare off into the distance so that your eyes diverge, then slip the stereo card up into view until your eyes accommodate a close focus. Vergence is distant, but accommodation is close, a combination that is not normal--a disparity--but it can also be an acquired skill. In our stereo camera club (disclaimer: I am tech editor of the non-profit club newsletter, Stereo Views, and run the Uptown3D.org web site), about half the members have learned to tolerate this disparity and "free view" stereo cards without glasses--but the other half complain of discomfort and give up. I suspect the same will be true for 3D TV. For some it will be a joy, and the others will just flip the from 3D-to-2D.